The present invention relates to communications satellites, and more particularly, to a coordinated system for satellite networks used to improve frequency reuse.
Satellites in geostationary orbit (GSO) have been widely preferred for several decades because of economic advantages. In a geostationary orbit, a satellite traveling above the Earth""s equator, in the same direction as that in which the Earth is rotating, and at the same angular velocity, appears stationary relative to a point on the Earth. These satellites are always xe2x80x9cin viewxe2x80x9d at all locations within their service areas. Antennas on Earth need to be aimed at a GSO satellite only once; no tracking system is required.
Coordination between GSO satellites generally occurs on a first-come, first-served, basis; such coordination sometimes is facilitated by governmental allocation of designated xe2x80x9cslotsxe2x80x9d angularly spaced according to service type.
Given the desirability of geostationary satellite orbits and technical limits in spacecraft and earth station design, the number of satellites that can effectively serve a given area on the earth using a particular band of operation (e.g., xe2x80x9cC-bandxe2x80x9d, or Ku-bandxe2x80x9d) is limited. While efforts have continued to improve the technology to enhance capacity, governments have on occasion resorted to auctions as a mechanism to assign limited orbital resources where the demand has exceeded the apparent supply. These circumstances have encouraged the development of complex and expensive new systems including those using low Earth orbit (LEO), medium Earth orbit (MEO), and higher frequencies, for example, the Ka band (up to approximately 40 GHz). Growth to higher frequencies is limited by problems of technology and propagation: thus some efforts at expanding satellite applications involve exploitation of the spatial dimension (i.e., utilizing satellite orbits other than the GSO. A host of proposed LEO and MEO systems exemplify this direction.
The recently filed LEO and MEO system applications, however, introduce additional technical complexity and costs that may not be justified in some applications. Frequency coordination and sharing are complicated by the unstructured criss-crossing of the lines of sight of these systems.
In the use of geostationary orbits, objectives in establishing networks is to maximize the independence between satellites. To achieve this, the burden of coordination is placed on the later entrant, to ensure interference-free operation vis-à-vis existing systems. Because of the number of networks in operation, particularly in the heavily utilized C-band and Ku-band, interference-free capacity is very difficult (if not impossible) to coordinate for service areas including the populated land masses. It would therefore be desirable to provide a system for coordinating various satellite operations so that the aggregate communications capacity of all satellites may be improved, and the overall utilization of the resource is increased. It would therefore be desirable to provide a system for coordinating various satellite operations so that the aggregate communications capacity of satellites may be maximized.
An object of the present invention is to provide a method for maximizing the aggregate capability of geosynchronous communications satellites for accommodating a multiplicity of services and/or providers.
Another object is to enable frequency reuse of spectrum used by geosynchronous satellites in an optimally coordinated manner, accounting for maximum number of requirements within a given band and geographical region.
A typical example of the invention, a satellite system has a plurality of orbit slots having a first orbital slot and a second orbital slot. A first satellite occupies a first orbital slot and generates a first set of beams. A second satellite in a second orbital slot generates a second set of beams. A tiling pattern results in a plurality of cells on the face of the Earth that defines all coverage areas to be served by the plurality of satellites. The beams of each satellite cover cells within its field of view that represent a subset of the overall tiling pattern. Each of the cells has a defined frequency sub-band for communication and is covered by a beam. The tiling pattern is generated in a way that allows frequency reuse, provides contiguous coverage, and minimizes interference between all satellites. The key parameters in determining interference and reuse are cell size and the related beamwidth, satellite arc spacing along with the related Earth station beamwidth, and the frequency reuse scheme. Other embodiments of this concept include more than two orbital positions (or xe2x80x9cslotsxe2x80x9d).
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.